Abbas *knows* that the Americans will feel obligated to veto this. What Abbas is relying on is that the Americans don't **want** to be put in that position i.e. Abbas is *relying* on the USA being desperate to stop that resolution ever getting to the floor of the UNSC. The price is well known: "the United States to articulate its support for the establishment of a Palestinian state within the 1967 borders". He wants THAT STATEMENT, and the threat of taking this to the UNSC is his way of getting it.
Australian police arrest 5 over shooting 'linked to terrorism' (Reuters)
from the article: Abbas may turn to Washington or UN to support state recognition